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V. On the Mechanical Appliances by which Flight is attained in the Animal Kingdom. 



By James Bell Pettigrew, M.JD. Edin., First Assistant in the Museum of the 

 Royal College of Surgeons of England, Ex-President of the Boy a I Medical Society 

 of Edinburgh, 8fc. Communicated by Professor Huxley. 



Read June 6th & 20th, 1867. 



(Plates XII.-XV.) 



INTRODUCTORY REMARKS. 



I^ T entering on the difficult and complicated subject of flight, I have found it advisable 

 to advert briefly to the movements of animals in general. I have adopted this course 

 from a belief that the movements of different animals, like the several orders of organized 

 beings, run into and are linked to each other by analogies and affinities at so many 

 points as to render the consecutive study of them in a measure compulsory. A careful 

 examination, moreover, of the movements and surfaces employed by quadrupeds and 

 fishes in traversing the earth and the water appears to me to supply the peculiar know- 

 ledge requisite for analyzing the unusually rapid oscillations of the wings. 



In the animal kingdom the movements are adapted either to the land, the water, or 

 the air; and, as a result, the instruments by which they are produced are specially 

 modified. This is necessary because of the different densities and the different degrees 

 of resistance furnished by the land, water, and air respectively. On the land the ex- 

 tremities of animals encounter the maximum of resistance, and occasion the minimum of 

 displacement. In the air, on the contrary, the pinions experience the minimum of resist- 

 ance, and effect the maximum of displacement, the water being intermediate both as 

 regards the degree of resistance offered and the amount of displacement produced. It 

 therefore requires a greater degree of muscular exertion to swim than to walk, and a 

 still greater one to fly. For this reason flight is the most laborious and, in some respects, 

 the most involved and intricate of all the animal movements*. 



Although all animals do not progress in exactly the same manner, there is neverthe- 

 less a similarity and a sequence in their movements which we shall do well to study. 

 This is proved by the fact that most quadrupeds swim as well as run, and some even fly ; 

 while many marine animals walk as well as swim, and birds and insects run, swim, and fly 

 indiscriminately. "When, however, the land-animals properly so called take to the water 

 or the air habitually, or the inhabitants of the deep seek the land or the air, or the insects 

 and birds which are more peculiarly organized for flight the earth and the water, their 

 organs of locomotion must possess those peculiarities of structure which characterize, 

 as a class, those animals which live on the land, in the sea, or in the air, as happens. 



* The efforts made by a bird in flying are always greatest in rising. When once fairly on the wing, flight is ren- 

 dered comparatively easy by the momentum which the body acquires being made to act in the plane of progression. 



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